1. Field of the Invention
This invention relates to a drive transmitting device for transmitting a drive force from a drive source such as a motor as required, and a sheet feeding device using the drive transmitting device.
2. Related Background Art
In a sheet feeding device used in an image forming apparatus or the like, a drive force from a drive source such as a motor is received to effect the rotation of a paper feeding roller and the vertical rocking of an intermediate plate on which sheets are piled. In this case, in order to effect the transmission of the drive force at predetermined timing as required, a drive transmitting device for selectively transmitting or not transmitting the drive force is provided in the course of the transmission route of the drive source between the drive source and the sheet feeding device.
As this drive transmitting device, there has heretofore been one using a partly untoothed gear having an untoothed portion having some of the teeth of the gear deleted. An example of the drive transmitting device using such partly untoothed gear will hereinafter be described with reference to FIG. 16 of the accompanying drawings.
The reference numeral 100 designates a drive transmitting device for selectively transmitting a drive force from a drive source, not shown, and the drive transmitting device 100 has a partly untoothed gear 102 and a driving gear 104 capable of meshing with this partly untoothed gear 102.
The driving gear 104 is connected to the drive source and is always rotated. The partly untoothed gear 102 is rotatively biased in a counter-clockwise direction as viewed in FIG. 16 by the resilient force of a coil spring 106. There is provided a solenoid 108 for stopping the partly untoothed gear 102 against the resilient force of the coil spring 106 in a position wherein the untoothed portion 102a of the partly untoothed gear 102 is opposed to the driving gear 104 (the state shown in FIG. 16). When this solenoid 108 is excited, an arm 108a moves from a position indicated by solid line in which it is engaged with the engagement portion 102b of the partly untoothed gear 102 to a position indicated by dots-and-dash line and the engagement is released, and the partly untoothed gear 102 is rotated by the coil spring 106 and comes into meshing engagement with the driving gear 104, whereby a drive force is transmitted from the driving gear 104 to the partly untoothed gear 102.
To make the meshing engagement at the start of the meshing engagement between the partly untoothed gear 102 and the driving gear 104 good, there is the technique disclosed in Japanese Patent Application Laid-open No. 6-50406.
This is a technique whereby in FIG. 16, the first tooth of the partly untoothed gear 102 which first meshes with the driving gear 104 is formed with an odd tooth inclined surface T1 cut away from the root of the front tooth surface in the direction of rotation toward the tooth top of the rear tooth surface, and the second tooth is formed with an even tooth inclined surface T2 cut away from the tooth top of the front tooth surface toward the root of the rear tooth surface.
By this construction, if the tooth tops of the gears are synchronized with each other (the tooth tops contact with each other) when in order to transmit the drive force from the driving gear 104 to the partly untoothed gear 102, the partly untoothed gear 102 is rotated by the coil spring 106 and comes into meshing engagement with the driving gear 104, a tooth of the driving gear 104 bears against the odd tooth inclined surface T1 of the tooth or the inclined surface T2 of the second tooth, of the partly untoothed gear 102, to thereby somewhat delay or quicken the rotation of the partly untoothed gear 102, whereby the meshing engagement between the tooth is reliably effected.
The above-described device according to the prior art, however, is good when the drive force is to be transmitted from the driving gear 104 side to the partly untoothed gear 102 side, but when the drive is to be transmitted from the partly untoothed gear 102 to the driving gear 104, the rotation of the partly untoothed gear 102 can not be delayed or quickened and therefore, there has arisen the problem that when the tooth tops contact with each other, a shock noise is produced or the tooth tops are damaged.